Principles of Spine Surgery

Ali FAhir Özer

Principles of Spine Surgery

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Table of contents

Intro

(ENTRANCE) History of Spinal Diseases and Spinal Surgery

1. The Embryology of Spine and Spinal Cord

2. Anatomy of Medulla Spinalis

3. Pain and Pain Pathways

4. Experimental Dimensions and Horizons in Spinal Surgery

5. Biology of Bone and Vertebrae

6. Growing Physiology of Vertebral Column

7. Motion Segment of the Spine

8. Biomechanics of the Normal Spine

9. Biomechanics of the Spine Degeneration

10. Biomechanical and Mechanical Testing of Spinal Implants

11. Sagittal Balance and Deformity

12. Spinal Implant and Biomechanics of Motion Preservation

13. Taking History and Patient Assessment in Spinal Surgery

14. Spinal and Peripheral Neurological Examination

15. Spinal Imaging Techniques

16. Informing the Patient, Complication and Malpractice

17. Standardization and Score-Scales in Spinal Surgery

18. Anaesthesia for Spinal Surgery

19. Patient Preparation and Surgical Positions

20. Incision, Retraction, Bleeding and Closing Management

21. Spinal Cord Monitoring

22. Robotic and Navigation Systems in Spine Surgery

23.The Clinical Application of Spinal Orthoses

24. Upper Cervical Region; Anterior Approach, Surgical Anatomy

25. Upper Cervical Region: Posterior Approach Surgical Anatomy

26. Surgical Anatomy of Lower Cervical Region and Cervicothoracic Junction: Anterior Approach

27. Surgical Anatomy of Lower Cervical Region and Cervicothoracic Junction: Posterior Approach

28. Thoracic and Thoracolumbar Anterior Approach: Surgical Anatomy

29. Posterior Approach to the Thoracic and Thoracolumbar Spine, Surgical Anatomy

30. Anterior Approaches to the Lumbar and Lumbosacral Spine, Surgical Anatomy

31. Posterior Approach to the Lumbar and Lumbosacral Junction; Surgical Anatomy

32. Topographic and Clinical Anatomy of the Pelvis

33. Types and Structures of the Implants

34. Physical Properties and Problems of Implants

35. Spinal Fusion and Fusion Materials

36. Spinal Fusion Techniques

37. Upper Cervical Instrumentation Techniques

38. Anterior and Posterior Instrumentation of the Lower Cervical and Cervico-Thoracic Junction

39. Thoracic and Thoracolumbar Instrumentation

40. Lumbar and Lumbosacral Instrumentation

41. Spinopelvic Instrumentation

42. Spinal Instrumentation for Deformity

43. Vertebroplasty - Kyphoplasty

44. Fixation Techniques In Osteoporotic Spine

45. Instrumentation in Degenerated Lumbar Vertebrae, Reduction and Stabilization in Spondylolisthesis

46. Cervical Arthroplasty

47. Lumbar Spinal Arthroplasty and Dynamic Instrumentation

Notes

Intro

Principles of Spine Surgery

Editors: Ali Fahir Özer, Ali Arslantaş, Sedat Dalbayrak

Co-Editors: İhsan Solaroğlu, Özkan Ateş

Publishers: Intertıp Yayınevi (Intertıp publishing house)

Copyright2016, Turkey

The scientific rights of this book and its contents belongs to the editors while rights pertaining to its printing, publication,distribution and sale belongs to İntertıp Publishers.

Unless written permission of the above mentioned persons and/or the publishers is obtained the whole or parts of this book cannot be reproduced and/or printed by means of mechanical, electronic, photocopying, magnetic paper and/or any other methods and cannot be distributed by any means or methods. Similarly, pictures, drawings and graphics contained in this book can not be used without permission of the publishers.

Editorial Coordinator: Hüseyin ÖZKAN

Project Coordinator: E. Armağan KARAAĞAÇLIOĞLU

Print-design-layout: İntertıp graphic workshop, İzmir

Print: Hermes Ofset Tanıtım

Date of Publication: 2016

İntertıp Yayınevi (Intertip publishing house)

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Customer service: +90 850 532 24 07

ISBN: 978-605-5004-12-5

ISBN: 978-605-5004-13-2

ISBN: 978-605-5004-11-8 (TK.)

Preface

Dear Colleagues,

Since the last 20 years, spinal surgery has a significant development in Turkey and around the world, compared with the other diciplines. Spinal surgery group was found ed with the support of Turkish Neurosurgical Society twenty years ago and now this small group has been transformed into a giant community with the idealism of trainers, trainees and volunteers. In this regard, we have learned, have tried to teach and have trained together while training. During our academic profession improve, spinal surgery in our country were subjected to quick scientific upgrade. Countless meetings, symposia, summer schools and conferences were organized. Numerous symposia books, course booklets we reprinted. Revealed a large number of valuable Works from each other.

In this book consists of two volumes, 100 chapters has been written by 110 aurthors. We are confident that this book which include thousands of references would be a seriouss our ceformany valuable papers. In this book, which includetrics of spinal surgery, we were at tempted to give the basic informations fluently and systematically. The spot informations about subject are provided in the each page.

We are very proud of writing first English work about spinal surgery in our country. Thanks and our gratitude is end less to all authors who contributed to both foreign, and native. We also thank to help ful editors Prof. Dr. İhsan Solaroğlu ve Prof. Dr. Özkan Ateş for their valuable additions in this book. We are confident that Turkish version of this book contributed substantially to many colleagues in our country.

Best wishes,

Prof. Dr. A.Fahir Özer

Prof. Dr. Ali Arslantaş

Doç. Dr. Sedat Dalbayrak

(ENTRANCE) History of Spinal Diseases and Spinal Surgery

Mehmet Reşid Önen, Sait Naderi

History of spinal diseases and spinal surgery is as old as history of medicine. The improvements in diagnosis together with the improvement of radiological imaging in the last century, improved internal fixation implants have brought spinal surgery to date. Some surgeries that are made with today’s technology have some Egyptian papyri that give information about antique medicine as well as other branches of medicine, and we have some knowledge we acquired from collections of Hippocrates. After the antique age, developments in medicine were interrupted as well, like in other disciplines in the Europe of the Medieval Age. During this period, medicine developed in the east, contrary to the west (96).

In this section, we will have an overview to the history of spinal surgery and analyze the brief history of especially spinal trauma, intervertebral disc, diagnosis, fusion and internal fixation. 

I. Diseases

1. Trauma

İmhotep (BC 2686-2613) He defined 48 osseous lesions related to the spine; defined ligamentous injury, vertebral subluxation and dislocation, and told that quadriplegia and paraplegia would occur in upper cervical and lower cervical injuries (60,136).

Hippocrates (BC 1460-1375) is the first physician who distinguished medicine from sorcery. He manufactured a traction device peculiar to him to reduct fractures and dislocations (3,100,120).

Galen (AD 130-200) Galen, who is from Pergamon, later moved to Rome and performed critical anatomical dissections and worked on subjects of experimental physiology and embryology. He is the most important name of antique medicine after Hippocrates. He defined the skeletal system and indicated the relation between the nervous system and the muscular system.

He designated the terms lordosis, kyphosis and scolosis. He made initiatives to correct these. He is deemed the world’s first sports physician since he was the official physician of Gladiators in Amphitheaters. Thus, he had the opportunity of doing several anatomic and neuro-physiologic studies in traumatic cases. He acknowledged the assessments of Imhotep and Hippocrates who argued that loss of motor and sense occurs under the lesion level as a result of cervical spinal cord injuries. He stated that different clinic entities could form in lesions of lower level. Galen is a physician, who performed dissection on Rhesus monkeys, as human dissection was prohibited during his period, except for trauma cases. However, he caused important mistakes in some matters as he identified the data he obtained from animal studies with human data and the impacts of these mistakes survived for some time (88,100,101).

Oribasius (AD 325-400) improved Hippocrates’s traction device and tried to reduct gibbus (106,107). 

Paulus of Aegina (AD 625-690) His essays in the last 1000 years were preserved. He emphasized the importance of usage of splint in spinal traumas. He is the first physician who applied laminectomy in treatment of fractures that make pressure (2,100,120).

Roland suggested traction with tapes between the body-pelvis and the neck in spinal traumas in his renowned work Chirurgica in 1210 (100,120,136).

Fabricius Hildanus performed reduction-traction process with the wedge-clamp system he installed in the spinous processes that he developed in cervical fracture dislocations in 1646. He suggested removal of fragments in case this maneuver failed (66,101,107).

Louis removed the metal fragment that entered the lumbar area and caused paraparesis with a successful surgery and ensured recovery (136).

Failed surgeries have been a reference for years for those who wanted to emphasize that surgery was a wrong approach. One of these surgeries is the failure of Cline in 1814 in a case with thoracic area fracture-dislocation. This result was presented as an evidence against operation in spinal cord injuries (136).

After those years, studies on therapeutic impact of traction increased.

In 1887 Bentecom introduced a traction system formed from adhesive tapes in which he applied weight up to 20 lbs (136). In 1929 Alfered Taylor addressed the importance of traction and ensured traction with a halter he placed between the mandibula and occiput (125). In 1933 Crutchfield introduced a newer traction device that can be implanted to the calvarium on the fracture-dislocation of the atlas. Crutchfield later modified this device and brought into a more practical form (29). In 1970s, Gardner’s device was introduced which didn’t require a hole to be bored in the head and after this introduction, in routine Crutchfield traction device was replaced by Gardner traction device in most places. On the other hand, traction devices made the patient bedridden and this required new tools aimed at fixation and traction. For this purpose, Nickel developed the Halo device in California for determining cervical fractures and for the traction of it, if necessary (103).

2. Lumbar Disc Herniations

Sciatica term was used by Shakespeare and it isn’t known when it entered the medical literature (117). Goldthwait informed the waist and leg pain of facets in 1911, Ghormley and Williams made suggestions regarding treatment (55,135).

Vesalius and Valleix described the anatomy and physiology of the disc in detail (131). In 1858 von Luschka defined a disc case that protruded to the posterior and illustrated lumbar disc herniation in his work titled half joint (Figure 1 and 2 A-B) (19,29,133). Babinski informed that Achilles reflex was lost in the painful side (14). In 1888 J.J. Forst, who was student of Charles Lasegue, defined Lasegue test (53,83). 

Discectomy case, which was informed for the first time, was performed transdurally by Krause in 1908. However, this case was named enchondromata (82).

Although various reasons were suggested on the matter of reasons of sciataalgia in early 20th century, in 1929 Dandy defined that disc derived nodules could cause neural pressure (Figure 3). Dandy named this situation as tumor in this important essay when making this definition in Archives of Surgery (32). Mixter and Bar achieved in correctly defining disc herniation for the first time (33,90,97). 

On 31 December 1932 Dr. Mixter and Dr. Wilson operated the extradural filling defect, which they established with myelography, and operated the first rupture disc herniation. At first phase they had assessed this mass as a tumor, but as a result of the anatomic, radiologic and microscopic studies performed on the spine by Schmorl and Junghanns, it was understood that it was nucleous pulposus (116). This case was first reported on 30 September 1933 by Dr. Mixter and Dr. Barr in New England Surgical Society (Figure 4) (136). In Figure 5 and 6 Dr. Mixter and Dr. Barr are represented.

After that year, lumbar disc surgery rapidly spread and the knowledge increased. In the mid 1930s, Dr. Love from Mayo Clinic indicated that the disc could be removed extradurally with laminotomy (86).

Once microscope was started to be used in neurochirurgia, Yaşargil and Caspar published microdiscectomy case series (25,138). Yaşargil performed discectomy without making medial facetectomy unlike Caspar and this is deemed the start of today’s microdiscectomy standard.

In 1974 Abdullah defined lateral discs (1). Kambin has been the pioneer in endoscopic disc surgery (75). 

3. Cervical Disc Herniation

First cervical disc surgery was performed in 1925 by Charles Elsberg (Figure 7) with posterior approach (48). Elsberg determined chondroma in a quadriparetic case that displayed similar characteristics (134). 

Defined cervical disc cases as tumor in these periods as well like in Lumbar disc herniations. Spurling and Segerberg, who defined cervical disc herniations in 1944, defined posterior foraminotomy in surgery of lateral discs in 1953 (120,136).

Thus, first surgical treatment of cervical disc herniations have been in the form of discectomy following lamikectomy and foraminotomy from posterior.

Anterior approaches could have been made in later years. Anterior approaches were used firstly for infection, in later years they were applied for cervical discs.

The first cervical interventions in the literature was made by otolaryngologists for large osteofits that lead to abscess or dysphagia (121). Discectomy techniques with different fusion were developed for cervical disc herniations by Smith-Robinson in 1955 (110), by Cloward in 1958 (26), by Bailey and Badgley in 1960 (15) and Hirsch (67) defined the non-fusion method in anterior cervical discectomy in 1960.

4. Lumbar Spinal Stenosis

Although it is known for a long time that the spinal narrow channel in horses causes Wobbler syndrome, it has taken very long time to understand spinal narrow channel in human. 

Portal stated in 1803 that small spinal channel could cause paraplegia (108). Sachs and Frankel informed a case that defined neurogenic claudication and cured with laminectomy in 1900 (113). In 1911 Bailey informed that a case with waist leg pain who could only walk by leaning forward and only short distances benefited from laminectomy (15). In 1931 Elsberg informed two cases that came with kauda equina due to thickened ligamentum flavum.

In 1946 Turkish surgeon Dr. Münip Sarpyener defined congenital lumbar spinal stenosis (Figure 8 and 9) (102,115). 

Verbist (Figure 10), who is a Dutch neurosurgeon, defined lumbar spinal stenosis in adults, and published this study in J Bone Joint Surg. (131). 

Cervical spinal stenosis was defined by Stookey in 1928 for the first time, however, he named this situation as ventral cervical chondroma (123). First surgical approaches were in the form of laminectomy and anterior techniques started in 1950s. In 1971 Hattori defined laminoplasty (64).

5. Spinal Tumors

Although there are no contradictions on the matter of first spinal tumor case removed with operation, it is accepted that first spinal tumor case was excised by Horsley (56).

In 1907 von Eiselsberg excised the first intramedullary tumor (132). In the last century Charles Elsberg performed the most comprehensive study on spinal tumors. Elsberg published the book titled "Diagnosis and treatment of surgical diseases of the spinal cord and its membranes" in 1916. Elsberg mentioned of spinal AVMs, syringomyelia and infections in this book (46-48).

6. Spinal Infections

First observations about spinal infections belongs to Hippocrates (3,67). However, the most enlightening study on this subject was carried out by Pott (109). Pott gave information about deformity and neurological deficit in a monograph he wrote in 1779 and suggested drainage of the abscess. First epidural abscess was determined by Delorme in 1894 after laminectomy. However, a successfully treated epidural abscess case was informed by Barth in 1901.

II. Diagnosis

No diagnostic study aimed at spinal diseases is found in the antique medicine period. The first studies on this subject were aimed at tuberculosis, which is a common pathology. First studies on this belongs to Morgagni, who is a modern pathologic anatomist. Although Morgagni informed several cases, the first tumor case that was removed with operation belongs to Maceven. Maceven removed a tumor which he called "fibrosis neoplasm of theca" with T5,6,7 laminectomy in 1883 (136). During this period, there were no radiologic diagnosis opportunities and this put forward the importance of neurological examination in finding out location of the lesion. Invention of x-ray machine in 1895 made a breakthrough in medicine (112).

German physicist Conrad Roentgen (1845-1923), who was born in the Netherlands, brought the x-ray tube to its final form on 8 November 1895 and ensured it to be put into usage. Conrad Roentgen (Figure 11) was awarded the Nobel prize for his work. 

After Corning defined lumbar puncture and Quincke popularized in in 1895 (120), Dandy defined pneumoencephaly in 1919. Since Dandy considered this method for assessment of cranial pathologies, this method was not used in assessment of spinal pathology (31).

Myelography, which was made by following administering of opaque matter by making lumbar puncture, was defined completely by coincidence one year later.

Sicard’s assistant Forstier notices that BOS comes while injecting Lipiodol into the facet joint are for waist pain. When Sicard made fluoroscopy in order to understand the patient’s condition, he defined the first myelography by coincidence (118). Later, he suggested Steinhausen Pantopaque instead of Lipiodol. With this substance, the application became a routin in diagnosis of tumor and disc diseases (122).

The first discography was defined by and put into usage by Lindblom in 1948. However, it wasn’t sought after for long years (84).

In 1972 Oldendorf, Hounsfield and Ambrose defined BT in diagnosis of spinal diseases (70,105). Hounsfield was awarded a Nobel prize for this in 1979 (70). In later years, Damadian defined spinal MRG (30).

III. Approaches

III. A: Anterior approach

III. A. 1: Cervical

Boudorf is the physician who used anterior cervical approach for abscess drainage for the first time in 1864 and Wright used it for tuberculosis abscess drainage for the first time in 1930 (20,137). The first cervical interventions in the literature was made by otolaryngologists for large osteofits that lead to abscess or dysphagia. Smith-Robinson applied anterior approach for cervical disc herniations in 1955 for the first time (110), Cloward applied in 1958 (26), Bailey and Badgley applied in 1960 (15).

III. A. 2: Thoracic

Due to problems related to negative pressure, anterior approach was developed the latest in the thoracic area. Tranthoracic approach was defined by Hodgson in 1956 (69).

III. A. 3: Lumbar

Müller applied anterior transperitoneal approach for the lumbosacral area with tumor pre-diagnosis in tuberculosis case in 1906 (89). First anterior interbody fusion was made by Burns in 1933 in spondylolisthesis case with graft taken from the sacrum (24), and in 1936 a similar operation was made by Jenkins with tibial graft (73).

Anterior approach was applied in a similar manner by Ito in 1934 for tuberculosis in paravertebral extraperithoneal manner (72). This approach was also used by Hodgson (69). 

III. B: Posterior approach

It is the oldest one among approaches aimed at the spine. The first approach on this subject was made by Egeli Paulus 1350 years ago (11) (2). The first cervical laminectomy performed after this case was made by Alban Smith in 1829 and this approach has been the most frequently used approach by surgeons for years (64) (119).

IV. Spinal Fusion and Internal Fixation

History of spinal fusion started almost with internal fixation applications. In general, wiring was used as the first fixation method and when the requirement of bone fusion was understood, fusion studies were concentrated on, whether instrument was used or not.

First fixation surgery was performed by Wilkins in 1887 by using wire in a baby due to thoracolumbar dislocation (120). Three years after this, Hadra performed wiring between C6-7 spinous processes in cervical Pott disease (Figure 12) (61). 

The first spinal fusion application, informed in the literature, was made in 1911 by Dr. Albee and Dr. Hibbs who inserted autologous tibia graft between spinous processes they divided in the middle (4,65). Campbell defined trisacral fusion and the technique of taking graft from iliac crest (136).

First screw usage was made by Dong King in 1944 by screwing facet (74). Boucher used the method of inserting screws within the pedicule with longer screws in 1959 (3) (136). The rod systems developed by Harrington (Figure 13) (63) were used in combination with wires (80). Humphries performed anterior fusion with anterior plate in 1961 (71). Roy-camille used pedicule screw and plate after 1963 (112), and Rene Louise used them as of 1972 (85).

Roy-Camille (Figure 14) used lateral mass screws in posterior cervical intervention in 1979. Galli and Brooks defined similar wiring and fusion methods for the purpose of atlantoaxial fusion (5,22,120,136). First odontoid screw was used by Böhler in 1982 (21).

Development of Spinal Surgery in Turkey

The history of neurosurgery in Anatolia dates back to the Ottoman period. Şerafeddin Sabuncuoğlu (born 1385), whose works survived to date and who performed several neurosurgery interventions as well as several surgical interventions, gave information about several operations in his work titled Cerrahiyyetü’l Haniyye and indicated the technique with miniature figures. Sabuncuoğlu mentions of reduction technique in fracture dislocations in his work (Figure 15) (44,49,50,94,129). 

Detailed medical records cannot be reached due to insufficiencies in archies in the last century. According to the current records, the first spinal intervention was made by Dr. Cemil Topuz (93). Before 1950s, basic spinal applications were performed by the first neurosurgeon and orthopedist Dr. Sarpyener (1029). Our first official neurosurgeons in the first half of the last century (1900-1949) are respectively Dr. Abdülkadir Cahit Tunay, Dr. Hami Dilek, Dr. Cemil Şerif Baydur, Dr. Ertuğrul Saltuk, Dr. Feyyaz Berkay, DrBülent Tarcan (40,59,124,128). 

In Turkey the adventure of neurosurgery starts in 1920s. Dr. Abdülkadir Cahit Tuner (1892-1983), who received education from Förester in 1923, (Figure 16) is the first official neurosurgeon. The first spinal tumor case performed by Dr. Tuner in Turkey is the intradural-extramedullary fibrom case at T9 level. He published this case he performed in 1924 in Istanbul Seririyatı Magazine in volume 4: issue 10. Dr. Tuner made level 5 laminectomy in the same years and issued an intradural psammom (85-87) (126-128). 

Dr. Hami Dilek returned to his country after receiving neurosurgery education from Vinvent and DeMartel in 1934 and became the second official neurosurgeon of our country (Figure 17) (1898-1989). Also Dr. Hami Dilek is the first neurosurgeon who received his specialty diploma from the Ministry of Health. Dr Dilek established the first neurosurgery service of Turkey in Haydarpaşa Numune hospital (6, 44). Dr. Dilek published several of his studies, and he also raised neurosurgeons who made several studies (34-39,77). 

Cemil Şerif Baydur, who received is specialty from Dr Vincent and returned to Turkey in 1937, published his book titled Neurosurgery Inquiries in 1937, which is the first neurosurgery book, and he wrote a chapter titled spinal cord pressures (trauma and tumors) (74).

Another Turkish neurosurgeon is Dr. Bülent Tarcan Dr. Tarcan worked in London between 1944-1952 and then obtained his certificate of specialty from the Ministry of Health in 1955. He translated Oliver’s Principles of Neurosurgery book into Turkish in 1954.

It is known that some neurosurgical operations were made in Ankara and Istanbul also by some general surgeons other than the neurosurgeons working in limited number of centers in first years of the Republic.

Ankara University took beds from Ankara Numune Hospital and Gulhane Military Medical Academy in 1945 and established the neurosurgery clinic. It is informed that the cases, the indication of which was made by Prof. Şükrü Yusuf Sarıbaş in this clinic, were operated by Prof. Dr. E. Melchior from the General Surgery clinic. It is known that these operations were limited with laminectomy and meningosel.

After Dr. Avman started working in Ankara University after 1960s, important operations were made in lumbar and cervical disc herniations, costotransversectotny, spinal cord tumors. (8-13,16,23,76). Dr. Avman et al. published 184 cord tumor cases they operated in 1976, 7 of which were made with microsurgery (12).

Though it is unclear when the first lumbar disc surgery was performed in Turkey, it is informed that Dr. Ege, Dr. Dilek and Ergüder made discectomy in these periods (17,18,42,43,51,114). Fusion surgery started in 1960s (42,43,91). Prof. Dr. Güngör Çakırgil started performing Harrington operation toward end on 1960s (57,58,98). It is known that fixation was made with wires in cervical instability in Ankara University after those years, (58). It is known that Dr. Vural Bertan performed cervical and thoracic corpectomy operations in Hacettepe University during the same years (58).

The Turkish Neurosurgery Association, which achieved in gathering Turkish neurosurgeons under a single roof, formed the spinal surgery group, like several other groups it formed under its structure, and made significant contributions to development of spinal surgery. The spine association, which was founded by spinal surgeons with orthopedics background, added spinal surgeons with neurosurgery background into its structure and carried out several national and international studies.

Today spinal surgery in our country has become capable of competing with the most advanced countries around the globe. Studies of Turkish spinal surgeons are increasingly included in world’s respectable literature day after day. 

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1. The Embryology of Spine and Spinal Cord

Mehmet Kanter, Tuncay Kaner

The formation of nerve system begins in the early stages of embryological period and continues after birth. These stages start with two important incidents in terms of development of nerve system: Gastrulation and Neurulation. With neurulation, the cells with primary neuron characteristics emerge. Differentiation, migration and proliferation of these cells, primarily the central nerve system forms. 

Early Embryological Development

Pre-gastrulation Stage

Before giving information on gastrulation, lets go through the first two weeks of development of embryo.

In the first week of embryo, fertilized zygot becomes two layered cell cluster with mitotic divisions. Outer cell mass will form trofoblast, inner cell mass will develop embryo itself. At this stage, embryo is known as blastosist.

In the second week of development, blastosist starts to embed into endometrium stroma. Trofoblast differentiates into two different layers. Later, the layers will form placenta and the connection between placenta-embryo. The inner cell mass (embryoblast) transforms into epiblast and hypoblast in order to establish two layer embryonic disc (bilaminar germ disk).

Gastrulation Stage

The third week of development is an important stage in development of central nerve system. This stage is known as gastrulation. A primitive streak is formed on surface of epiblast and becomes more recognizable as primitive groove in 15th and 16th days. Cranial end of primitive streak originates primitive node. At middle of this node, the small depression is called primitive pit. Primitive node initiates embryological development of central nerve system and peripheral nerve system.

In transverse cross-sections from primitive groove of germ disc, a new layer is observed forming between epiblast and hypoblast. Epiblast cells migrate along primitive groove and move under epiblast. This inward movement is called invagination. The layer formed with migrated cells is called intraembryonic mesoderm. In the end of gastrulation, embryo transforms into the embryonic disc formed from 3 germ layers (ectoderm (old epiblast), mesoderm, endoderm (old hypoblast)) (Figure 1). 

The Formation of Notochord

Invaginated epiblast cells from primitive pit migrate till prechordal plate and construct a median cellular cord, called notochordal process. The primitive pit forms notochordal canal in notochordal process. Mesoderm and notochordal process separate two layers throughout the disc, except prochordal plate and cloacal membrane in caudal end of primitive streak, expanding between ectoderm and endoderm.

In 18th. day, notochordal process unites with floor endoderm. With the disappearance of the lumen of notochordal canal, notochordal process becomes thin cellular plate. After disappearance of notochordal base, a temporary canal is formed between the yolk and amniotic sac cavities, called neuroenteric canal.

At the same time, the intact ceiling of notochordal canal forms a flat plate bending inward from edges, this plate is called notochordal plate. Cells forming notochordal plate proliferate startinging from cranial edge and forms a cellular rod, called notochord. After formation of notochord, floor endoderm remains intact layer and notochord becomes a continuous cord. The neuroenteric canal connecting amniotic and yolk sacs disappears.

At the end of three weeks, notochord settles lengthening from chloacal membrane to prochordal plate.

At the beginning, the germ layer ectoderm was a flat disk large in the cranial end and narrower in the caudial end, resembling a slipper. The developing notochord induces roof ectoderm. Ectoderm thickens and forms neural plate. Thus, neurulation begins. Ectoderm in the region of neural plate is called neuroectoderm.

The slipperlike neural plate enlarges and extends through primitive streak. At the end of third week, lateral edges of neural plate establishes neural folds growing more and rises. This formation develops neural groove.

Formation of neural plate, neural folds and neural canal is called neurulation. 

Neural folds start to move together and fuse eachother in direction of cephalocaudal and in the middle line of neural plate, thus forms neural tube.

At the beginning, neural tube is in connection with amniotic cavity, from cranial end via anterior neuropore, from caudal end via posterior neuropore.

Anterior neuropore disappears in 25th day, posterior neuropore disappears in 27th day and neural tube becomes a closed tube. In the future, from neural tube, central nerve system will be developed.

Brain vesicles will be formed from cranial end of neural tube which is larger region and medulla spinalis will be formed from caudal region which is narrower.

The Development of Somite and The Differentiation Mesodermal Germ Layer

Intraembryonic mesoderm, at the beginning, is seen as a layer in two sides of middle line with thin and loose structure. During the development of notchord and neural tube, 17th day, mesoderm cells proliferate and thicken. It is called paraxial mesoderm.

Each paraxial mesoderm, continues through two sides as intermediate mesoderm and lateral mesoderm.

In lateral mesoderm, small spaces are formed and coalesce to form a single cavity called intraembryonic coelom.

In the middle of third week, paraxial mesoderm begins to divide into pair structures called somite. The first somite pair, in 20th day, is seen in cervical region of embryo and extending in craniocaudal direction ends with 42-44 pair with developing 3 pairs everyday till end of 5th week.

These, 4 occipital, 8 cervical, 12 thoracal, 5 lumbar and 8-10 coccygeal pair somites. First occipital and last 5-7 coccygeal somites disappear. The other somites, form the axial skeleton of embryo. The age of embryo is determined with the number and age of somites in this term (Figure 2 and 3).

The Differentiation of Somites

At the beginning of 4th week, somites acquire a lumen called myocell. Cells in lateral and ventral wall of each somites obtain polymorphic appearance having more loose structure. These polymorphic cells are called sclerotom and forms mesenchym or early connective tissue. This early connective tissue wrapping medulla spinalis and notochord forms columna vertebralis.

Dorsal wall of each somite is called dermatom. Dermatom forms myotom which is cellular plate with light color nucleus.

Mytom of each somites, form muscles of somite segments . Dermatom cells, losing epithelial feature, extend under surface ectoderm and forms skin dermis and subdermal tissue.

Formation of Medulla Spinalis (Spinal Cord)

Neural tube in the caudal region of 4th pair somites will be developing medulla spinalis. In 9th and 10th week, the side walls of neural tube thicken and the tube becomes smaller, forms canalis centralis. Neuroepithelial cells on the wall of neural tube, forms ventricular zone(stratum ependimale). The outer layer of neuroepithelial cells, marginal zone, will be forming white matter of medulla spinalis with developed axons originated from spinal ganglions and brain. Some neuroepithelial cells originated from ventricular zone transforms into pirmer neurons, neuroblasts. These cells form a new layer, intermediate zone (stratum palliale) between ventricular and marginal zones. 

The first supportive cells of central nerve system, glioblasts, originate from neuroepithelial cells after formation of neuroblasts and migrate from ventricular zone into intermediate and marginal zones. Some cells will differentiate into astroblasts to form astrocytes. Some cells will differentiate into oligodendroblasts to form oligodendrocytes. After developing neuroblasts and glioblasts, neuroepithelial cells form ependim cells which cover the central canal. 

In the 6th and 9th weeks, with the proliferation and differentiation of neuroepithelial cells, the medulla spinalis wall thicken, floor and roof becomes thinner. In the thickened wall, at two sides, two longitudinal grooves are produced which is named sulcus limitans. This groove develops alar plate (lamina alaris) in the dorsal region, basal plate (lamina basalis) in the ventral region. These plates cause longitudinal buldges along medulla spinalis. The separation of plaques are important in terms of their afferent and efferent functions.

Alar plates constitute dorsal grey columns along medulla spinalis. Neurons in this colons have afferent nucleus. The cell bodies in basal plate constitute ventral grey column and lateral grey column. In the development process of basal plates, between ventral edges ventral median septum (septum medianum ventrale), at the same region in the ventral surface, a deep groove is developed, ventral median fissur.

The cells developing spinal ganglions are T-shape unipolar neurons and originate from neural crest (crist neuralis). The two tails of neurons have axonal features but since the signal move through peripheral tail to cell body, it has a function of a dendrite. Peripheral extensions proceed to spinal nerves and form sensory endings. Central extensions enter medulla spinalis via dorsal roots (Figure 4). 

The Embryological Development of Spine

In all vertebrates, primer skeleton is originated from corda dorsalis (notochord). In hurman, after mesenchymal term, the cartilage term starts and later spine goes through ossification. Consequently, in human, notochord is seen in only embryological period. Notochord is required to develop spine. The impulses from chorda dorsalis induce development of somites from dorsal mesoderm. Ectoderm responses these impulses forming neural plate whereas mesodorem responses with segmentation.

Sclerotome and myotome place at the same level. If a spine from each sclerotome was developed, a muscle should be developed from each myotom to attach to the spines. However, to conduct the spine, each muscle should bind to two spines from below and above. To fulfill this process, a groove emerges in the middle of sclerotome. This is called intrasegmental groove. Later, using this groove, sclerotome is divided into cranial and caudal parts. Cranial cells show looser formation. After a sclerotome is divided into two, cranial part of the sclerotome fuse with the caudial part of previous sclerotome and forms blastem. These blastems are real sketch of vertebrates. Later, since the straited muscle developed from somites binds to two different vertebrae, they secure the movement of the vertebral column. 

The embryological development of spine are divided into three phases. 1) Mesenchymal Phase (Epithelial-mesenchymal Interaction). 2) Cartilage Phase (Condensation). 3) Ossification Phase (Differentiation). However, after birth, spine continues to develop.

Mesenchymal Phase

The development of vertebral column begins with accumulation of mesenchymal cells around notochord. In 4th week of embryological development, mesenchymal cells gather in three main regions. 1) Around notochord 2) Around neural tube 3) Wall of corpus

Cartilage Phase

In 6th week of embryological development, mesenchym condenses into chondrification centers in mesenchymal vertebrae. In each centrum, two centers associate and form cartilaginous centrum. At the same time, centers vertebral archs unite each other and centrum. With the extension of cartilaginous centrum in vertebral arches, the spinous and transverse outgrowth emerge.

In this period, chorda dorsalis becomes narrower as a result of pressure of cartilage. Only in the level of intrasegmental grooves, this pressure is not as high as the other region. Accordingly, in this level chorda dorsalis remains larger. This section will construct nucleus pulposus. Later, the other part of chorda dorsalis in the level of vertebrea, disappears and nucleus pulposus remains. In this chondrification phase, vertebrae has the body and mesechym facing back. From 4th embryonic month, the sides are closed. If this closure is not completed, rachischisis occurs.

Ossification Phase

The calcification of vertebral column begins in embryological development and continues till age 25. Bone developes from two different tissues: Cartilage and mesenchym.

Prenatal Phase

In the beginning, there are two primary ossification center in centrum. These centers exist in ventral and dorsal vertebrae. At the end of embryological development, all ossification centers merge into one center. At the end of embryological term, three primary ossification centers exist. One of these centers is found in centrum, the other two are found in two sides of vertebral archs. 

References

Moore KL, Persaud TVN: The Developing Human: Clinically Oriented Embryology, Philadelphia, 2003: 60-71, 382-385, 428-434

Sadler TW: Langman’s Medikal Embriyoloji. Başaklar C (çev), Ankara: Palme Yayıncılık 1993 

2. Anatomy of Medulla Spinalis

Emre Özkara, Ali Arslantaş

Medulla spinalis (spinal cord) is the part of central nervous system in the vertebral canal, beginning at foramen occipitale magnum and extending down toward the caudal end. It is cylindrical in shape and ends around the L3 vertebral level in the newborn and at the lower side level of L1 in the adult. It is a little longer in the male than in the female; the average length in the male adult is about 45 cm Medulla spinalis merges with medulla oblangata at the foramen occipitale magnum at the base of the skull (1). 

Medulla spinalis is protected by three layers of meninges which are continuation of the meninges covering the cerebrum. These are, from outward to inward, dura mater spinalis, arachnoidea mater spinalis, and pia mater spinalis. The dura mater spinalis and arachoidea mater spinalis end at the vertebral level of the second sacral vertebra. Pia mater spinalis ends at the lower end of medulla spinalis, forming filum terminale after this level. Filum terminale merges with dura mater after the vertebral level of the second sacral vertebra forming ligamentum coccygeum and ends by attaching to the coccyx. Medulla spinalis has grooves in the ventral and dorsal sides. Fissura mediana anterior in the ventral side is deeper than sulcus medianus posterior in the dorsal side. Also there are two pairs of other sulci on right and left sides, namely, sulcus anterolateralis on the front surface and sulcus posterolateralis on the back surface of the spinal cord.

The inner structure of medulla spinalis: Medulla spinalis is made of gray matter, a neuropile nucleus in the center, and of white matter which is located outside of the gray matter and consists almost totally of axons. The gray matter consists of cell bodies and dendrites of spinal neurons and unmyelinated axons. White matter consists of longitudinal columns or tracts of axons (2). Like other regions ofcentral nervous system, the white matter of medulla spinalis is made of axons, neuroglia, and blood vessels. It surrounds the gray matter and is white due to high number of myelinated axons (3). The quantities of gray and white matters differ with medulla levels. The white matter in the cervical region is relatively thick, but gradually loses from its mass as medulla extends downward. The gray matter is thickest in servical and lumbar enlargements, consisting of neurons responsible for motor and sensory functions of the extremities. The enlargements are fusiform enlargements which are called intumescentia cervicalis and intumescentia lumbosacralis, respectively (2).

The gray matter is formed by axons of neurons, neuroglia, and blood vessels. In the anterior column, most of the neurons are large and multipolar. Their axons originate from the anterior roots as alpha afferents innervating skeletal muscles. The smaller neuromuscular spindles exit as gamma efferents innervating intrafusal muscle fibers. The medial group is found in most segments and is responsible fort he innervation of the skeletal muscles of neck and torso; the central group is present in some cervical and lumbosacral segments (nucleus nevri phrenici, n. nervi accesorii, n. lumbosacralis); the lateral group is located in the cervical and lumbosacral segments and is responsible fort he innervation of skeletal muscles. In cross-sections, the projections (horns) of the gray matter, anterior column and posterior column, bound by gray commissure which holds canalis centralis in the middle, form the gray H. There is a small columna lateralis in thoracic and upper lumbar segments. There are 4 groups of neurons in columna posterior. The substantia gelatinosa is located on the apex of the posterior horn of gray matter and is associated wth the senses of pain-heat and touch. The nucleus proprius constitutes the bulk of the dorsal horn and receives fibers that are associated with the senses of position and movement (proprioception), two-point discrimination, and vibration. The nucleus dorsalis (Clarke’s column) is located from the C8 to L3-L4 levels and is an important structure for proprioception. The visceral afferent nucleus is located from T1 to L3 levels and is associated with visceral afferents. The columna lateralis is located from T1 to L2 or L3 levels and extends preganglionic sympathetic nevre fibers. There is also a similar group of neurons in the S2-3-4 segments from where preganglionic sympathetic nevre fibers originate (3).

Canalis centralis runs longitudinally through the length of the entire spinal cord. It is continuous with the canalis centralis of the distal half of m. oblongata and with the fourth ventricle. The central canal expands forming the terminal ventricle which is located at or near conus terminalis. The terminal ventricle is filled with cerebrospial fluid and lined with ependymal cells which are ciliated columnar epithelial cells. The Rexed laminae is a system of nine layers of gray matter identified by Rexed. The laminae are designated with Roman numbers starting from the posterior horn and extending toward the anterior horn (I-IX). The gray matter surrounding the central canal is designated as Lamina X (4).

The white matter can be divided into anterior, lateral and posterior funiculi. The anterior funiculus lies between the anterior median fissure and the most lateral of the anterior nevre roots; the lateral funiculus lies between the exit of these roots and the postero-lateral sulcus; and the posterior funiculus lies between the posterolateral sulcus and the posterior median sulcus (3).

Among afferent nerves there are fasciculus gracilis and fasciculus cuneatus which carry fine and characteristic senses from the upper and lower parts of the body. Crude senses and senses with higher threshold are carried by anterior and lateral spinothalamic tracts; the lateral spinothalamic tract is particularly important in transmitting pain and temperature. Among other afferent tracts closely associated with reflex activity and motor control are posterior and anterior spinocerebellar, spinoolivary, spinotectal, and spinoreticular tracts (2). The efferent tracts can be divided into two groups:

The first group includes the corticospinal tracts and the rubrospinal tract. This group preferably ends at the dorsolateral parts of the spinal cord, which hold the neurons controlling the distal muscles of the extremities. The damage of these tracts results in a loss of the ability to perform fine movements. The second group includes the anterior and lateral reticulospinal tracts which extend in the medial longitudinal fasciculus and preferably end in the ventromedial regions of the spinal cord, tectospinal tract, lateral and medial vestibulospinal tracts, and interstiospinal tract. These regions hold the neurons that control the muscles of axial and proxymal extremities. Damage in this area often results in disturbances in posture and straightening up